1. To make less bright or to be less alert or keen; that is, to become or to cause something to become less clear, distinct, bright, or shiny: "The fog dulled the morning for a few hours until the sun came out."

"Special earplugs dulled the sound of the chain saw."

2. To make something; such as, a feeling less sharp, not as strong, or reduces severity: "The medication dulled her mind and hampered her thinking skills; however, it was also dulling her pain."

3. To become or to cause something; such as, a knife or blade to become less sharp: "This knife has been dulled because of so much usage."